Generally an internal combustion engine will comprise a cylinder block provided with one or more cylinders, each of which receives a piston connected to a crankshaft journaled in the cylinder block by respective connecting rods.
Each of the cylinders may be asssociated with inlet and outlet ports or passages which can be provided with valves, connected to intake and exhaust manifolds, and generally is provided in the region of fluid passages through which a lubricant such as the engine oil and a coolant, such as water or antifreeze solution can be circulated. The ends of the cylinders are closed by cylinder heads which may be bolted to the cylinder block and, to seal the assembly and especially the various fluid passages and compartments from one another, a more or less compressible cylinder head gasket is provided between the cylinder head and the cylinder block and is traversed by the bolts while being provided with an array of ports, cutouts and orifices through which the fluid communication can take place and around which the gasket can seal one fluid passage from another.
The cylinder head gasket thus must perform a number of functions:
Firstly, it must seal the liquid coolant, the liquid lubricant and the gas passages from one another.
Secondly, it must be able to seal the combustion gas within the cylinder at the elevated pressures and temperatures generated by the firing process.
Thirdly, this gasket must constitute a shim, spacer or thickness regulator for the gap between the cylinder head and the engine block, the two elements which are bolted together through the gasket and between which the gasket is sandwiched.
Fourthly, the gasket must serve as a compensating element compensating for geometric irregularities of the sealing faces of the cylinder head and the cylinder block so that the sealing relationship is maintained in spite of manufacturing tolerance deviations and in spite of deformations which occur in operation because of thermal effects or other mechanical distortions.
The gasket must be resistive to heat, must have considerable compressive strength, but must be somewhat yieldable to fulfill these requirements.
Numerous composite gasket structures have been proposed with various drawbacks. For example, fluid sealing can be effected by sandwiching an asbestos plate between a pair of metal foils or sheets (linings), the asbestos plate being reinforced by a perforated metal foil or sheet which is embedded therein and forms a core through the apertures of which the asbestos mass can extend. This embodiment of earlier gasket constructions has been found to be excellent when the two faces which are to be sealed relative to one another, namely, the face of the cylinder head and the face of the block, have excellent planarity and the thermal cycling of the engine does not impose significant constraints on the seal, i.e. the engine parts in contact with the seal are not significantly distorted by the thermal conditions.
In another prior art configuration, around the liquid passages, beads of a yieldable material, such as a silicone can be provided usually below or inwardly of the metal linings which bulge outwardly in the regions of these beads. The beads can be molded independently of the asbestos plate or can be molded onto it.
In still another system, a screen-printing approach has been utilized to apply special sealing beads or cords around the liquid apertures. These beads form annular bulges on the upper and lower surfaces of the gasket, generally of a rounded convex profile.
The beads or cords of these latter systems have been found to resist compression poorly and generally become unsatisfactory and rupture after some use because of thermal cycling and the distortions generally associated therewith.